This invention relates to switching power supplies, and more specifically relates to a novel switching power supply having a constant output voltage produced from a wide range of input a-c voltages using a single MOSFET transistor for the switching circuit.
Voltage regulators are well known for producing a constant output voltage, usually d-c, from a source of unregulated input a-c voltage. One form of regulated power supply is a switching power supply circuit which contains a rectifier for rectifying the input line voltage of the power supply; an inverter circuit for producing a relatively high frequency output voltage from the rectified line input; and a pulse width modulator for varying the pulse width of the output of the high frequency inverter. The pulse width modulated high frequency output is then rectified and applied through suitable filters to produce a controlled output voltage. A suitable feedback circuit is provided between the output circuit and the pulse width modulating circuit to vary the pulse width as necessary to maintain a given output voltage.
The switching power supply circuit described above can be used as a universal power supply for operation from a-c power line voltages which are, for example, nominally 115 volts in the United States, and 220 volts or 240 volts in Europe. However, input circuit modifications must be made when the circuit is converted either to a 115 volt system or a 220/240 volt system to produce a given regulated output circuit.
The requirement for switching the input circuit configuration when the power supply circuit is operated at one end or the opposite end of its input voltage range increases the complexity of the circuit and increases its cost.
The present invention provides a novel circuit configuration for a switching power supply which has a sufficiently wide regulation range as to enable the production of a given output voltage, whether the input voltage is a nominal 115 volts power line input or a nominal 240 volts power line input without input circuit switching. The invention further permits the use of a single MOSFET transistor as the transistor switch for the switching power supply.